[Mr. INTJ]

Howdy,

I think my question is about impedance matching, so I'm asking it
here...

Some time ago I bought a Sony F-V620 dynamic mic (specs below) to do
some recording on my PC. The problem is that I have to max out the
gain and practically kiss the mic to get a decent sound level. I'm
about to whip out the soldering iron and build a little preamp, but I
wanted to check with the folks here before I do.

Here are some specs:

Sony F-V620

Polarity: Unidirectional
Impedance: 600 ohms
Effective Output Level: -55.8 dBm
Link:
http://reviews.cnet.com/microphones/...-20648859.html

The microphone has a gold "mini" jack that is plugged directly into
the microphone input - I'm not using an adapter of any kind. I've
tried comparing with a headset mic, to see if the input level is more
reasonable, but the results were inconclusive... you're *supposed* to
have the headset mic a few mm away from your lips, so yeah, it's
louder, but so is the other mic if I'm right on top of it.

I've looked up the specs online for my soundcard (SoundBlaster Audigy
2 ZS), but it just says "Microphone in"; nothing about impedance. Can
anyone shed some light on why the mic level is so low, and whether
building a preamp is a reasonable approach to solving this problem?

Thanks

Mr. INTJ
San Diego, CA

[Anahata]

On Mon, 18 Aug 2008 01:12:42 -0700, Mr. INTJ wrote:

I think my question is about impedance matching

Level matching, more likely.
In simple terms, it just isn't loud enough. Your computer sound card is
designed for a mic that generates high output for a given sound level,
and dynamic mics produce low output.

whether
building a preamp is a reasonable approach to solving this problem?

Yes, you need a preamp, and if your sound card has a "line" input you
should then connect the preamp's output to that, and not use the
computer's mic input at all.

--
Anahata
==//== 01638 720444
http://www.treewind.co.uk ==//== http://www.myspace.com/maryanahata

[Ian Thompson-Bell]

Mr. INTJ wrote:
Howdy,

I think my question is about impedance matching, so I'm asking it
here...

Some time ago I bought a Sony F-V620 dynamic mic (specs below) to do
some recording on my PC. The problem is that I have to max out the
gain and practically kiss the mic to get a decent sound level. I'm
about to whip out the soldering iron and build a little preamp, but I
wanted to check with the folks here before I do..

Check the sound card set up. Many have a +20dB gain switch for the mic
input.

Cheers

Ian

[Eeyore]

anahata wrote:

Mr. INTJ wrote:

I think my question is about impedance matching

Level matching, more likely.
In simple terms, it just isn't loud enough. Your computer sound card is
designed for a mic that generates high output for a given sound level,
and dynamic mics produce low output.

whether
building a preamp is a reasonable approach to solving this problem?

Yes, you need a preamp, and if your sound card has a "line" input you
should then connect the preamp's output to that, and not use the
computer's mic input at all.

100% agreed.

Graham

[Scott Dorsey]

In article ,
Mr. INTJ wrote:
Howdy,

I think my question is about impedance matching, so I'm asking it
here...

Some time ago I bought a Sony F-V620 dynamic mic (specs below) to do
some recording on my PC. The problem is that I have to max out the
gain and practically kiss the mic to get a decent sound level. I'm
about to whip out the soldering iron and build a little preamp, but I
wanted to check with the folks here before I do.

Typical soundcard inputs aren't intended for use with regular microphones.
There are multiple issues, including the DC offset, the operating levels,
and the fact that they are unbalanced.

Interface circuits can be found in:

1. Solving Sound Card Microphone Problems, Michael Covington, QST, June 2000

2. A Dynamic Microphone Soundcard Amplifier, Paul Lowenstein, AudioXpress,
Feb 2008.

I have not used either of these circuits so I can't say which is better,
but the Lowenstein circuit should have a lower output impedance.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Badmuts]

I'm
about to whip out the soldering iron and build a little preamp

Hey, that's the spirit! :-)

These days people easily spend $200 on a mixer just to get a preamp. Nobody
solders anymore or builds the greatest preamp for $10 in parts and an
afternoon of soldering.

I should get back into soldering, probably.

Bm
(just spent $3-digit-number on a couple of neumann mics)

[Badmuts]

"Badmuts" wrote in message
...
These days people easily spend $200 on a mixer just to get a preamp.

Coming to think of it... these days people even spend $3000 on a preamp that
doesn't even contain a mixer.

Weird business.

Bm

[Mike Rivers]

Badmuts wrote:

These days people easily spend $200 on a mixer just to get a preamp. Nobody
solders anymore or builds the greatest preamp for $10 in parts and an
afternoon of soldering.

That's indeed the spirit, but a $200 mixer can look pretty good in
comparison when you consider the time to shop for parts, make a case,
add a power supply, and cut holes for the connectors and controls. You
can build a mic preamp into a Radio Shack project box in an afternoon if
you have more tools than a soldering iron, but it will probably have to
be battery powered unless you're pretty clever.

It was so much easier to build stuff like this with tubes,
point-to-point wiring, and a well stocked junk box.

--
If you e-mail me and it bounces, use your secret decoder ring and reach
me he
double-m-eleven-double-zero at yahoo -- I'm really Mike Rivers
)

[Scott Dorsey]

Mike Rivers wrote:
Badmuts wrote:

These days people easily spend $200 on a mixer just to get a preamp. Nobody
solders anymore or builds the greatest preamp for $10 in parts and an
afternoon of soldering.

That's indeed the spirit, but a $200 mixer can look pretty good in
comparison when you consider the time to shop for parts, make a case,
add a power supply, and cut holes for the connectors and controls. You
can build a mic preamp into a Radio Shack project box in an afternoon if
you have more tools than a soldering iron, but it will probably have to
be battery powered unless you're pretty clever.

It was so much easier to build stuff like this with tubes,
point-to-point wiring, and a well stocked junk box.

It still is, and there's no reason not to build stuff like that with tubes
and point to point wiring.

Although I will say that expresspcb.com makes it pretty cheap and easy to
do far more sophisticated stuff at your kitchen table.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Richard Crowley]

"Mr. INTJ" wrote ...
...Sony F-V620 dynamic mic

Not really made for the typical computer mic input.
Output is simply too low (as you have accurately
surmised.)

... I have to max out the gain and practically kiss
the mic to get a decent sound level.

Built-in computer mic inputs assume you are using
a (relatively) hotter electret condener mic.

....
The microphone has a gold "mini" jack that is plugged directly into
the microphone input - I'm not using an adapter of any kind.

Note that the mic (pink) input has "bias power" (3-5VDC)
on the "ring" which is intended for powering the electret
condenser mic capsule.

I've
tried comparing with a headset mic, to see if the input level is more
reasonable, but the results were inconclusive... you're *supposed* to
have the headset mic a few mm away from your lips, so yeah, it's
louder, but so is the other mic if I'm right on top of it.

It is virtually certain that any headset designed for computer
use has an electret condenser mic capsule in it. And that has
much higher output than your Sony F-V620.

I'm about to whip out the soldering iron and build a
little preamp, but I wanted to check with the folks
here before I do.

Since you have the 3-5VDC available at the ring of the
input jack, it should be almost trivial to make a 1-transistor
amplifier stage to boost the signal by 20-30dB and power
it from the "bias power". You can likely snag a circuit on
www.epanorama.net

Of course, remember that the typical built-in mic
preamps are nothing to write home about. They are
adequate for low-quality speech commuications, but
any more ambitious application likely needs a real
external preamp feeding the line-level input of the
computer. (And note that few, if any, portable PC's
are fitted with line-level inputs.)

[Richard Crowley]

"Scott Dorsey" wrote...

It still is, and there's no reason not to build stuff like that with tubes
and point to point wiring.

Although I will say that expresspcb.com makes it pretty cheap and easy to
do far more sophisticated stuff at your kitchen table.

If you don't want to fool around with caustic chemicals and
photolithography in your kitchen (or garage), and you don't
need 24-hour turn times, you can get boards from a place
like www.batchpcb.com in 3-4 weeks for $10 setup and
$2.50/sq in for 2 layer, and $8/sq in for 4 layer. This is
commercial-quality stuff with plated-thru holes, solder mask
both sides, etc. As the name implies, they batch the incoming
orders into standard panel size and then have it fabbed in China.

Or if you have panel-size orders, check out places like
www.olimex.com in Bulgaria. They do mail-order business
around the planet (as to many Chineese vendors.)

[Paul Stamler]

"Mike Rivers" wrote in message
newsnkqk.192$UX.175@trnddc03...
Badmuts wrote:

These days people easily spend $200 on a mixer just to get a preamp.
Nobody
solders anymore or builds the greatest preamp for $10 in parts and an
afternoon of soldering.

That's indeed the spirit, but a $200 mixer can look pretty good in
comparison when you consider the time to shop for parts, make a case,
add a power supply, and cut holes for the connectors and controls. You
can build a mic preamp into a Radio Shack project box in an afternoon if
you have more tools than a soldering iron, but it will probably have to
be battery powered unless you're pretty clever.

It was so much easier to build stuff like this with tubes,
point-to-point wiring, and a well stocked junk box.

Naah, it's about the same (if you use wire-wrap IC sockets). The connections
are just closer together, and we're older. And, perhaps, less likely to have
the right stuff in the junk box.

Oh, and it was tough to power tube stuff off batteries unless you were
willing to spend inordinate amounts of money on an A and B battery.

Peace,
Paul

[Richard Crowley]

"Mr. INTJ" wrote ...
I'm about to whip out the soldering iron and build a little preamp,
but I wanted to check with the folks here before I do.

I love breaking out the soldering iron and building little gadgets,
adapters, cables, etc. But to be honest, for an application like
this one, I'd be just as inclined to get a little $5 amp board like...
http://www.sparkfun.com/commerce/pro...oducts_id=8704

[Arny Krueger]

"Badmouths" wrote in
message
I'm
about to whip out the soldering iron and build a little
preamp

Hey, that's the spirit! :-)

These days people easily spend $200 on a mixer just to
get a preamp.

Really? A $39.00 Behringer from the nearest GC store will do the job just
fine.